Originally Posted by
TheBusFlyer
Hello everyone,
Could someone please explain me which value of thrust is computed by the AT THR mode on the triple when the aircraft is flying in VNAV SPD during descend? I understand in VNAV SPD, the aircraft controls the speed using the elevators…but why does the AT command IDLE at some given time…and THR at other? Is THR commanded when we are below the flight path to not ‘dive’ in idle and therefore not increase our profile to the calculated path?
Did not find anything in the FCOM regarding this subject.
Thanks!
Hey,
In VNAV SPD mode during descent, the autothrottle (AT) adjusts engine thrust to control speed. It usually goes to IDLE thrust when the plane is on or slightly above the descent path to prevent speeding up. When the plane is below the descent path or needs to slow down, it commands THR thrust to control the descent rate and match the profile.
I get your frustration about not finding info in the FCOM, but sometimes real-world experience or insights from others can fill in the gaps.
Hope this helps!
Mark Smith